For fostering an industry that can continuously grow, implementation of a new energy generation/distribution system that can achieve both highly efficient energy consumption and reduction of industrial wastes has been socially demanded. Construction of a new energy and communication fusing network intended to generate or distribute energy is in progress in various places in the world. The energy and communication fusing network aims to link various pieces of equipment that are engaged in generation, distribution, and consumption of energy, share pieces of information concerning the operating situations of the pieces of equipment and an ambient environment among all the pieces of equipment or specific pieces of equipment, control the operating states of the pieces of equipment, which are linked over the network, using the pieces of information, and optimize the performances, which all the pieces of equipment linked over the network should attain, as an entire system. For implementation of the network, since the number of pieces of equipment to be linked is very large, use of a wireless network is expected in order to reduce a cost of introduction of the network and a cost of maintenance of the network.
The wireless network is expected to reduce the costs of introduction and maintenance but is confronted with such issues that it is easy to intercept or alter data, which flows over the network, because of a physical nature of an electromagnetic wave serving as a communication medium for wireless communication, and that it is difficult to control the pieces of equipment using the data or sustain the security of monitoring information. In particular, if the pieces of equipment linked over the energy and communication fusing network generate or distribute a resource, which is directly connected to civilian lives, such as electric power, tap water, or gas, malicious interception or alteration of the data would give a severe blow to the civilian lives. The issue that it is difficult to control the pieces of equipment or sustain the security of monitoring information has to be resolved without fail in order to implement the energy and communication fusing network with a wireless technology.
Wireless communication is achieved along plural different paths that extend from a transmitting point to a receiving point, that is, plural multipath reflection propagation paths derived from reflections caused by pieces of equipment because the pieces of equipment existent between the transmitting point and receiving point of communication act as electromagnetic wave scattering bodies. The plural paths derived from multipath reflections are intrinsic to the transmitting point and receiving point. At any spatial point other than the transmitting and receiving points, a signal sent from the transmitting point reaches another spatial point along paths different from the paths extending from the transmitting point to the receiving point. A signal generated at any spatial point reaches the receiving point along paths different from the paths extending from the transmitting point to the receiving point. This brings about a possibility that information which cannot be obtained at any spatial point may be transferred between the transmitting and receiving points by selecting or combining plural paths extending from the transmitting point to the receiving point. As a technology employing this principle, Patent Literature 1 is cited. A frequency spectrum of a receiving signal is used as a key to encrypt information that should be transmitted, and the information is transmitted from the transmitting point. At the receiving point, the receiving signal is decrypted using the frequency spectrum. Patent Literature 2 describes that the behavior of receiving electric power which temporally fluctuates and is called a delay spread in mobile communication is used as a key to encrypt information that should be transmitted, and the information is transmitted from the transmitting point. At the receiving point, the receiving signal is decrypted using the delay spread. Further, Patent Literature 3 describes that a transmitter transmits an impulse train, an impulse response intrinsic to the receiving point is used as a key to encrypt information that should be transmitted, and the information is transmitted from the transmitting point. At the receiving point, the receiving signal is decrypted using the impulse response. Due to the reversibility of an electromagnetic wave and the symmetry of transmitting and receiving in communication, whether a signal wave on the same time base is transmitted from the transmitting point to the receiving point or from the receiving point to the transmitting point, the signal wave of the receiving signal is held unchanged. The signal wave stems from interference of an electromagnetic wave that is transmitted over plural transmission lines derived from intrinsic multipath reflections and formed between the transmitting and receiving points. Therefore, it is very difficult to acquire the signal wave at any spatial point other than the transmitting and receiving points.